Author(s): Menglu Qin; Daisuke Harada; Shinji Egashira

Linked Author(s):

Keywords: Rainfall sediment runoff; Hillslope erosion; Sediment transport process; Sediment sorting process; Sediment runoff modeling

Abstract: This paper numerically investigates the effects of sediment supply from hillslope erosion on sediment transport processes in a river basin. A conceptual sediment path for the hillslope area along the slope direction was proposed and incorporated into a rainfall and sediment runoff model (RSR-model) to implement a mechanics-based sediment transport theory for estimating hillslope erosion. Then, by re-evaluating Manning's roughness of the sediment path based on the grain size of its surface sediment to minimize the effect due to inappropriate flow resistance of the surface flow resulting from the distributed rainfall-runoff analysis process. Thus, these procedures allow the model to estimate the fine sediment erosion and transport by surface flows on hillslopes using the same method applied to estimate suspended sediment flow in rivers. Two cases were calculated in the Abira River basin (300 km2) in Hokkaido, Japan, rainfall associated with four typhoons on 8/8-9/7,2016: Case1, which considered hillslope erosion process, and Case2, which did not. Case1 was in better agreement with the observed sediment size distribution of the riverbed and the suspended sediment concentration in the river flow. The simulation results interpret that the supplied sediment is partially and temporarily deposited on the riverbed and gradually alters the discharge and texture of both bed sediment and suspended sediment flows throughout the channel network by affecting channel conditions such as elevation and sediment size distribution of the riverbed. This suggests that sediment supply from hillslopes is critical in shaping long-term sediment dynamics in the river basin.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1223-cd

Year: 2023